Knowledge of wind conditions at a given location is desirable in many applications. Taking sailing as an example, generally speaking, sailing is the art of using wind to control the motion of a vessel on a body of water. Among the factors that affect sailing is the sail and its interaction with the wind.
A sail functions as a foil with properties similar to the wing of an aircraft. It is well known that air moves faster where the wind strikes the sail. Faster moving air induces lower pressure on the sail. Conversely, slower moving air produces more pressure on the sail.
As is well known from the Bernoulli principle the difference in pressure will cause movement from a region of high pressure to a region of low pressure. Thus, the difference in the pressure on opposing sides of a sail induces the movement of the sail boat.
It is known that a sail boat cannot be induced to move if it is headed directly into the wind. However, it can, with the help of its keel, move upwind. Whether a sail will act as a foil to propel the vessel depends on the direction of the wind relative to the sail and the consequent pressure differential (speed differential) created to induce movement.